1. Field of the Invention
This invention relates to the reduction of tangential and radial stress in a suspension element of a loudspeaker transducer. The suspension element, such as a surround or spider, is designed to increase its ability to expand in both the radial and tangential directions.
2. Related Art
Sound reproduction devices such as loudspeakers are utilized in a broad range of applications in many distinct fields of technology, including both the consumer and industrial fields. Sound reproduction devices utilize a combination of mechanical and electrical components to convert electrical signals, representative of the sound, into mechanical energy that produces sound waves in an ambient sound field corresponding to the electrical signal. Thus, variations of electric energy are converted into corresponding variations of acoustic energy, i.e., sound.
Traditional speakers convert the electric energy to sound with one or more drivers that produce sound waves by rapidly vibrating a flexible cone or diaphragm. A diaphragm is usually circular with a central cone-shaped and/or dome-shaped portion that is coupled to a cylindrical former having a coil wire wrapped around the cylinder. Generally, the coil or wire is wrapped around the exterior side of the cylindrical former. The combination former and coil shall be referred to as the “voice coil.” The voice coil is typically suspended by a “spider,” which is attached to the frame of the speaker. The spider holds the voice coil in position while allowing it to move freely back and forth. The exterior edge of the diaphragm is attached to the frame of the speaker via a surround. Both the spider and the surround generally act as a rim, made of flexible material that spans between the voice coil and the frame and the diaphragm and the frame, respectively.
The surround and the spider act to form the suspension system that positions the voice coil and allows the voice coil to move relative to a transducer magnet(s) when electrical current is directed to the voice coil. The suspension allows the voice coil to rapidly move up and down along the longitudinal axis and vibrate the diaphragm. The suspension needs to be flexible enough to allow for the movement of the voice coil and diaphragm while at the same time keeping the diaphragm from wobbling or becoming “de-centered.”
Generally, suspension designs are concerned with minimizing the radial stress of the surround caused by the movement of the voice coil and diaphragm. The surround generally has a uniform half circular cross-sectional shape that extends to the entire perimeter or circumference of the surround, when the surround is generally circular. Thus, the radius of the half circular cross-section of the surround remains constant along the perimeter of the surround, creating an arched or dome shaped rim about the speaker. Similarly, the spider has a uniform cross-section that extends to the entire perimeter of the spider. The cross-section of the spider generally forms uniform corrugations, where the peaks and valleys, i.e., ridges and grooves, typically are of the same radius. For purposes of this application, the terms perimeter and circumference shall be synonymous and may be used interchangeably to define the perimeter of the suspension elements, regardless of their shape.
When the diaphragm of the speaker is vibrated, the external edge of the diaphragm moves up and down along the longitudinal axis of the speaker. During both the up-stroke and down-stroke of the voice coil, the surround is extended from its resting position to accommodate the movement of the diaphragm and the spider is extended to accommodate the movement of the voice coil. Thus, as the voice coil moves up and down, the cross-sectional shapes of the surround and spider elongate. As the voice coil moves up and down, both radial and tangential stress is placed upon the suspension elements, i.e., the spider and the surround. The radial stress is caused by the extending of the suspension elements in a direction parallel to the outer and inner edges of the suspension elements. The tangential stress, also referred to as “hoop stress”, is the stress placed on the suspension elements in a direction perpendicular to the outer and inner edges of the suspension elements. It is the tangential and radial stress on the suspension elements that limits the excursion and stiffness of the diaphragm and movement of the voice coil.
The extent to which the suspension elements limit the amount of excursion of the diaphragm and the movement of the voice coil is dependent upon the size of the suspension elements. The bigger the suspension elements, the more the suspension elements can stretch and allow the diaphragm and voice coil to move more freely. Employing bigger suspension elements, is not, however, a viable solution in a smaller speaker design since the size of the diaphragm must be significantly reduced to accommodate a larger suspension. When a small surround is utilized the excursion of the diaphragm is reduced, limiting the performance of the speakers. Thus, a trade off is made between performance and size when utilizing small speakers, such as those speakers found in laptop computers or small electronic devices. A need therefore exists to design speaker systems having suspension elements that increase the excursion of the diaphragm and allow more movement of the voice coil by reducing the radial and tangential stress placed on the suspension elements. While addressing this need would help to increase the performance of small speakers, any size speaker could experience increased performance capabilities from such a design.